docs(buttons): add boolean badge

Author: Foxandxss

src/buttons/docs/readme.md

@@ -32,7 +32,7 @@ With the buttons directive, we can make a group of buttons behave like a set of
   An expression that evaluates to a truthy or falsy value that determines whether the `uncheckable` attribute is present.
 
 * `uncheckable`
-  _(Boolean attribute)_ -
+  <small class="badge">B</small> -
   Whether a radio button can be unchecked or not.
 
 ### Additional settings `uibButtonConfig`